Catalytic hydrogenation of aromatic aldehydes



Patented June 30, 1936 UNITED STATES PATENT OFFICE CATALYTIC HYDRCGENATION OF AROMATEC ALDEHYDES William J. Amend, Wilmington, E. I. du Pont de Nemours &

Del, assignor to Company, Wilmington, Del., a corporation of Delaware No Drawing.

11 Claims.

obtain alcohols when hydrogenating with a 15 nickel catalyst. The

temperatures at which they operated caused the formation of hydrocarbons. Sabatier (Catalysis and Organic Chemistry- Sabatier and Reid, Section 388) states:

Contrary to what takes place with aliphatic aldehydes the hydrogenation of aromatic aldehydes over nickel does not reduce them to alcohols, but tends to replace the oxygen by hydrogen, Hz, to give the aromatic hydrocarbons, which below 250 C. may be more or less hydrogenated to the cyclohexane hydrocarbons. There is, at the same time, some decomposition of the aldehydes into the hydrocarbons and carbon monoxide. Thus between 2l0-235 C. benzaldehyde gives toluene and methyl cyclohexane together with small amounts of benzene and cyclohexane It is an object of this invention to produce ring-substituted aromatic alcohols from the corresponding aldehydes by means of catalytic hydrogenation, employing ferrous metal catalysts. It is a further object of the invention to carry out these reactions at relatively low temperatures.

Investigation of the existing processes for the hydrogenation of aldehydes has led to the discovery that the hydrogenation of ring-substituted aromatic aldehydes to the corresponding alcohols may be accomplished successfully in the presence of ferrous material, preferably nickel, catalysts at relatively low temperatures. So far as I am aware the processes of my invention, as applied to the ring-substituted aromatic aldehydes specified, have not been known or disclosed before. The following examples set forth preferred embodiments of my invention, and are presented for purposes of illustration and not as limitations.

Example I A charge consisting of 104 g. of anisaldehyde and 10 g. of nickel chromite catalyst was placed Application Serial No. 739,736

August 14, 1934,

in a shaking autoclave and agitated at -80 C. and at a hydrogen pressure of 2000 lbs. per sq. in. for three hours. Upon separation of the reaction products there was obtained 12.5% unreduced anisaldehyde, 60% of crude anisyl alcohol, and 46% of pure anisyl alcohol based on the theoretical yields.

Example II One hundred grams of vanillin in 100 g. of absolute ethyl alcohol, together with 10 g. of nickel catalyst, prepared by digesting a nickelaluminum alloy with caustic soda, was placed in a shaker tube and agitated at 40-50 C. at a hydrogen pressure of 2000 lbs. per sq. in. for two hours. The reaction products were taken up in additional alcohol and benzene and filtered. A yield of vanillyl alcohol was obtained by crystallization from the solvent. The crystals of alcohol were fairly pure as indicated by their melting point, Ill-113 C.

Example III A charge consisting of g. of piperonal, 100 g. of water, and 10 g. of nickel catalyst prepared by digesting a nickel-aluminum alloy with caustic soda, was placed in a shaking autoclave and agitated at 50-70" C. and at a hydrogen pressure of 1500 lbs. per sq. in. for fifteen minutes. An 81% yield of piperonyl alcohol crystals was obtained by crystallization from the reaction products after the addition of a small quantity of ethanol. The melting point of the crystals was ti l-55 C.

Powdered ferrous metal catalysts are suitable for the processes of this invention, and they may be prepared by precipitating a chromate, carbonate, or hydroxide of the metal, followed by reduction with hydrogen, although I do not limit the invention to these methods. The ferrous metals are preferably employed as catalysts in conjunction with inert supports such as kieselguhr, pumice, active carbon, silica gel, and the like. Finely divided metallic nickel is the preferred catalyst and may be prepared in an active form by a number of alternative methods.

The preferred method consists of reduction with hydrogen of oxygen-containing nickel compounds such as the carbonate, oxide, hydroxide, or salt of an inorganic acid such as chromic acid, vanadic acid, tungstic acid, etc. Suitable temperatures for the reduction of such nickel compositions are found in the range 250-500 C. Ammonia or other reducing agents may be used. When reducing chromates by heat alone or together with hydrogen, chromites are formed which serve as the support for the catalytic hydrogenating metal. A preferred catalyst is also prepared by. the digestion of a nickel-aluminum alloy with caustic soda according to the Haney method as described in U. S. P. 1,628,190.

Temperature of hydrogenation is an important factor in the success of the processes of this invention, as relatively low temperatures are necessary to obtain alcohols from the aromatic aldehydes. I prefer to employ temperatures in the range 40-80 C. but may operate at temperatures from -110 C. 7

Elevated pressures are required for the processes herein described. I prefer to operate at pressures from 1500-3000 lbs. per sq. in., but'a wider range of pressures may be employed, say from 500 lbs. per sq. in. to an upper limit determined only by the strength of the reaction vessel. Application of the processes of this invention is limited 'to the class of compounds designated as ring-substituted aromatic aldehydes. Aldehydes. included under this classification, in addition to those previously mentioned in the examples, are: methylsalicylic, benzoylsalicylic, and cinnamic aldehydes; and methyl, ethyl, acetyl, and benzoyl derivatives of vanillin. These aldehydes may be hydrogenated either alone or in the presence of solvents such as alcohol, benzene,

to be understood that I do not alcohols than have cyclohexane, etc. i

The processes of my invention offer more practical and economical means of obtaining valuable heretofore been practiced. By operating'at temperatures below 110 C., the formation of undesired hydrocarbons is eliminated. The ring-substituted aromatic alcohols which I obtain may be used in the manufacture of perfumes, cosmetics; and drugs. the alcohols may possibly be used as flavoring materials to a limited extent.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is limit myself to the specific embodiments thereof except as defined in the appended claims. i

I claim:

1. The process of hydrogenating an aldehyde selected from the class consisting of anisaldehyde, vanillin and piperonal which comprises ature between 25 and 110 ature between 25 and 110 C. and at a hydrogen Certain of contacting the aldehyde and hydrogen in the presence of a ferrous metal catalyst at a temper- C. and at a hydrogen pressure in excess of 500 lbs. per sq. in.

2. The process. of hydrogenating an aldehyde selected from the class consisting of anisaldehyde, vanillin and piperonal which comprises contacting the aldehyde and hydrogen in the presence of a ferrous metal catalyst at a temperpressure of 1500 to 3000 lbs. per sq. in.

'3. The process according to claim 1 in which the hydrogenation reaction is carried out in the presence of an inert solvent for the aldehyde.

4. The process according to claim 1 in which 1 the hydrogenation reaction is carried out at a temperature of 40 to 80 C.

5. The process according to claim 1 in which the catalyst is a nickel containing catalyst.

6. The process of hydrogenating anisaldehyde to form anisyl alcohol which comprises contact-' ing anisaldehyde and hydrogen in the presence of a nickel chromite catalyst at a temperature of 70 to 80 C. and under a hydrogen pressure of 2000 lbs. per sq. in.

7. The process of hydrogenating vanillin to form vanillyl alcohol which comprises contacting vanillin and hydrogen in the presence of a hydrogenating catalyst.

8. The process of hydrogenating vanillin to form vanillyl alcohol which comprises contacting vanillin and hydrogen in the presence of a ferrcus metal catalyst.

53. The process of hydrogenating vanillin to form vanillyl alcohol which comprises contacting vanillin and hydrogen in the presence of a nickel catalyst.

form piperonyl alcohol which comprises contacting a solution of piperonal in water with hydrogen in the presence of a nickel containing catalyst at a temperature of to C. and at a hydrogen pressure of 1500 lbs. per sq. in.

- WILLIAM J. AMEND. 5 

